Thermoelectric generator

ABSTRACT

Disclosed are apparatus and methodology for constructing thermoelectric devices (TEDs). N-type elements are paired with P-type elements in an array of pairs between substrates. The paired elements are electrically connected in series by various techniques including brazing for hot side and/or also cold side connections, and soldering for cold side connections while being thermally connected in parallel. In selected embodiments, electrical and mechanical connections of the elements may be made solely by mechanical pressure.

PRIORITY CLAIM

This application claims the benefit of previously filed U.S. ProvisionalPatent Application entitled “THERMOELECTRIC GENERATOR,” assigned USSN61/789,505, filed Mar. 15, 2013, and which is incorporated herein byreference for all purposes.

FIELD OF THE SUBJECT MATTER

The presently disclosed subject matter relates to devices for convertingthermal energy to electrical energy generators. More particularly, thepresently disclosed subject matter relates to thermoelectric generators(TEGs) and methodologies for constructing such devices usingelectrically coupled doped semiconductive ceramic elements to generateelectricity based on temperature differences between portions of thecoupled elements.

BACKGROUND OF THE SUBJECT MATTER

The presently disclosed subject matter generally concerns improvedcomponent design for generating electrical energy based on thePeltier/Seebeck effect.

Known references that include examples of features for thermallygenerating electricity include U.S. Pat. No. 5,288,336 to Strachan etal. entitled “Thermoelectric energy conversion,” U.S. Pat. No. 5,430,322to Koyanagi et al. entitled “Thermoelectric element sheet in whichthermoelectric semiconductors are mounted between films,” U.S. Pat. No.6,005,182 to Imanishi et al. entitled “Thermoelectric conversion moduleand method of manufacturing the same,” U.S. Pat. No. 6,091,014 to Eklundet al. entitled “Thermoelectric materials based on intercalated layeredmetallic systems,” U.S. Pat. No. 7,351,906 to Yotsuhashi et al. entitled“Method of manufacturing crystalline film, method of manufacturingcrystalline-film-layered substrate, method of manufacturingthermoelectric conversion element, and thermoelectric conversionelement,” U.S. Pat. No. 7,888,583 to Lagally et al. entitled“Semiconductor nanowire thermoelectric materials and devices, andprocesses for producing same,” and U.S. Pat. No. 7,942,010 to Bell etal. entitled “Thermoelectric power generating systems utilizingsegmented thermoelectric elements.”

In addition, examples of U.S. Published Patent Applications that includefeatures for thermally generating electricity include U.S. Pub2010/0031986 to Okamura entitled “Thermoelectric Module,” U.S. Pub2010/0116308 to Hayashi et al. entitled “Thermoelectric conversionelement, thermoelectric conversion module, method for producingthermoelectric conversion element,” U.S. Pub 2010/0132755 to Uchida etal. entitled “Thermoelectric Conversion Material, Method for Producingthe Same, Thermoelectric Conversion Device and Method of ImprovingStrength of Thermoelectric Conversion Material,” U.S. Pub 2011/0016888to Haas et al. entitled “Thermoelectric Module,” and U.S. Pub2011/0088737 to Nakamura et al. entitled “Thermoelectric conversionmodule and method for manufacturing thermoelectric conversion module.”

While various aspects and alternative features are known in the field ofthermoelectric electrical energy generation and related methods formanufacture, no one design has emerged that generally addresses all ofthe issues as discussed herein. The disclosures of all the foregoingUnited States patents and published patent applications are hereby fullyincorporated into this application for all purposes by virtue of presentreference thereto.

SUMMARY OF THE SUBJECT MATTER

In view of the recognized features encountered in the prior art andaddressed by the presently disclosed subject matter, improved apparatusand methodology for generating electrical energy using multi-layerceramic elements have been developed.

In an exemplary configuration, thermoelectric modules are constructed bycoupling n-type and p-type materials as individual elements to formpairs connected in series electrically, in parallel thermally, andconnecting such pairs in an electrically series, thermally parallelconfiguration.

In exemplary such configurations, the n-type material may in someembodiments be based at least in part on SrTiO3 while the p-typematernal may in some embodiments be based on NiO material. Bothmaterials may incorporate doping materials including, for example, Nband La with the SrTiO3 and Li with the NiO material. They are producedusing various standard ceramic processing techniques, with smallvariations allowing greater control and enhancement of electricalproperties.

The use of ceramic processing to create these elements has theadvantages of simplicity and versatility over typical preparationtechniques for common thermoelectric elements. For example, manycommercial thermoelectric semiconductor materials (for example, bismuthtelluride) are produced by common single crystal preparation methods(Czochralski method or zone refining) which are applicable to a morelimited materials set, and do not allow microstructural engineering asdescribed herein. On the other hand, ceramic processing as currentlypracticed can be used on a wide variety of compositions and allowslayer-by-layer control of composition and microstructure. Furthermore,thick and thin film techniques can be easily utilized to produceterminations which are conducive to the high temperatures whichthermoelectric element will see.

A thermoelectric module may be created by sandwiching pairs of then-type and p-type elements in such a way as to form a plurality of pairsof elements electrically connected in series while being thermallyconnected in parallel.

In one present exemplary embodiment, a thermoelectric device forconverting thermal energy to electrical energy based on temperaturedifferences between portions of the device preferably comprises aplurality of N-type oxide ceramic elements; a plurality of P-type oxideceramic elements, respectively paired with such plurality of N-typeelements; a pair of supporting ceramic substrates, supporting aplurality of conductive traces thereon, and with such paired N-type andP-type elements received on selected of such conductive traces so as toform an array of such pairs between such substrates; and at least onepair of connection terminals provided on at least one of suchsubstrates, for the connection of leads thereto. In such exemplaryembodiment, preferably such paired elements are electrically connectedin series by such conductive traces and thermally connected in parallelrelative to such substrates, so that generated electricity may beconducted from such array based on temperature differences betweenportions of such paired elements based on the Peltier/Seebeck effect.

In another present exemplary embodiment, a thermoelectric device forconverting thermal energy to electrical energy using electricallycoupled doped semiconductive ceramic elements to generate electricitybased on temperature differences between portions of the device,preferably comprises a plurality of N-type elements, each comprising adoped semiconductive oxide ceramic element; a plurality of P-typeelements, each comprising a doped semiconductive oxide ceramic element,respectively paired with such plurality of N-type elements; a pair ofsupporting ceramic rings forming concentric radial configurations havinga generally open central portion adapted for exposure to a heat sourcewith the exterior portion of the thermoelectric device adapted forexposure to an environment cooler than such heat source, and with suchpaired N-type and P-type elements received on selected portions of suchceramic rings so as to form a radial array of such pairs; and electricalconnections for electrically connecting such paired elements in serieswhile such paired elements are thermally connected in parallel relativeto such ceramic rings, so that generated electricity may be conductedfrom such array based on temperature differences between portions ofsuch paired elements based on the Peltier/Seebeck effect.

In yet another exemplary embodiment, a thermoelectric generator modulefor converting thermal energy to electrical energy using electricallycoupled doped semiconductive ceramic elements to generate electricitybased on temperature differences between portions of the module based onthe Peltier/Seebeck effect, preferably comprises a plurality of N-typeelements, each comprising a doped semiconductive oxide ceramic element;a plurality of P-type elements, each comprising a doped semiconductiveoxide ceramic element, respectively paired with such plurality of N-typeelements; an opposing pair of generally planar supporting ceramicsubstrates, supporting a plurality of complementary conductive tracesthereon, and with such paired N-type and P-type elements received onselected of such conductive traces so as to form an array of such pairssandwiched between such substrates; and at least one pair of connectionterminals provided on at least one of such substrates, for theconnection of leads thereto. In such exemplary embodiment, preferablysuch paired elements are electrically connected in series by suchconductive traces and thermally connected in parallel relative to suchsubstrates, so that generated electricity may be conducted from sucharray via such connection terminals based on temperature differencesbetween portions of such paired elements.

Those of ordinary skill in the art from reviewing the presentlydisclosed subject matter will appreciate that such disclosure isintended to encompass both apparatus and corresponding and/or associatedmethodologies. One exemplary method relates to methodology forgenerating electrical energy based on the Peltier/Seebeck effect usingoxide ceramic elements by providing a thermoelectric module constructedby coupling N-type and P-type materials as individual elements to formpairs electrically connected in series and thermally in parallel betweenopposing supporting substrates.

In another present exemplary embodiment, such method may relate tomethodology for manufacturing a thermoelectric generator module forconverting thermal energy to electrical energy using electricallycoupled doped semiconductive oxide ceramic elements to generateelectricity based on temperature differences between portions of themodule based on the Peltier/Seebeck effect. Such methodology maycomprise providing an opposing pair of generally planar supportingceramic substrates, supporting a plurality of complementary conductivetraces thereon; placing an array of plural paired N-type elements andP-type elements in electrical communication with such conductive tracesso that the paired elements are electrically connected in series by suchconductive traces, such elements each comprising a doped semiconductiveoxide ceramic element, and such that such elements are thermallyconnected in parallel relative to such substrates; and attaching atleast one pair of connection terminals on at least one of suchsubstrates, for the connection of leads thereto, so that generatedelectricity may be conducted from such array via such connectionterminals based on temperature differences between portions of suchpaired elements.

Another present exemplary embodiment of presently disclosed methodologyrelates to a method of providing a thermoelectric device for convertingthermal energy to electrical energy based on temperature differencesbetween portions of the device. Such an exemplary method may preferablycomprise forming respective pluralities of N-type and P-type oxideceramic elements; providing a pair of ceramic substrates with aplurality of predetermined conductive traces thereon; respectivelypairing and aligning such N-type and P-type elements on selected of suchconductive traces so as to form an array of such pairs electricallyconnected in series and captured between such substrates and thermallyconnected in parallel between opposing determined hot and cold sidesthereof; and forming at least one pair of connection terminals on atleast one of such substrates, for the connection of leads thereto, sothat generated electricity may be conducted from such array based ontemperature differences between such hot and cold sides based on thePeltier/Seebeck effect.

Yet another presently disclosed exemplary method relates to a method ofmaking a thermoelectric device for converting thermal energy toelectrical energy using electrically coupled doped semiconductive oxideceramic elements to generate electricity based on temperaturedifferences between portions of the device, comprising forming aplurality of N-type elements, each comprising a doped semiconductiveoxide ceramic element; forming a plurality of P-type elements, eachcomprising a doped semiconductive oxide ceramic element, respectivelypaired with such plurality of N-type elements; providing a pair ofsupporting ceramic rings forming concentric radial configurations havinga generally open radially central portion adapted for exposure to a heatsource with the radially exterior portion of the thermoelectric deviceadapted for exposure to an environment cooler than such heat source;placing such paired N-type and P-type elements on selected portions ofsuch ceramic rings so as to form a radial array of such pairs; andelectrically connecting such paired elements in series while such pairedelements are thermally connected in parallel relative to such ceramicrings. Per such exemplary method, generated electricity may be conductedfrom such array based on temperature differences between portions ofsuch paired elements based on the Peltier/Seebeck effect.

Additional objects and advantages of the presently disclosed subjectmatter are set forth in, or will be apparent to, those of ordinary skillin the art from the detailed description herein. Also, it should befurther appreciated that modifications and variations to thespecifically illustrated, referred and discussed features and elementshereof may be practiced in various embodiments and uses of the presentlydisclosed subject matter without departing from the spirit and scope ofthe subject matter. Variations may include, but are not limited to,substitution of equivalent means, features, or steps for thoseillustrated, referenced, or discussed, and the functional, operational,or positional reversal of various parts, features, steps, or the like.

Still further, it is to be understood that different embodiments, aswell as different presently preferred embodiments, of the presentlydisclosed subject matter may include various combinations orconfigurations of presently disclosed features, steps, or elements, ortheir equivalents (including combinations of features, parts, or stepsor configurations thereof not expressly shown in the figures or statedin the detailed description of such figures). Additional embodiments ofthe presently disclosed subject matter, not necessarily expressed in thesummarized section, may include and incorporate various combinations ofaspects of features, components, or steps referenced in the summarizedobjects above, and/or other features, components, or steps as otherwisediscussed in this application. Those of ordinary skill in the art willbetter appreciate the features and aspects of such embodiments, andothers, upon review of the remainder of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the presently disclosed subjectmatter, including the best mode thereof, directed to one of ordinaryskill in the art, is set forth in the specification, which makesreference to the appended figures, in which:

FIG. 1 illustrates an exemplary assembly process for constructingthermoelectric generators (TEGs) in accordance with the presentlydisclosed subject matter;

FIGS. 2A-2C illustrate an alternative embodiment of the presentlydisclosed subject matter employing screen-printed substrates;

FIGS. 3A-3D respectively provide alternative exemplary configurations ofan exemplary thermoelectric device in accordance with the presentlydisclosed subject matter.

Repeat use of reference characters throughout the present specificationand appended drawings is intended to represent same or analogousfeatures, elements, or steps of the presently disclosed subject matter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As discussed in the Summary of the Subject Matter section, the presentlydisclosed subject matter is particularly concerned with improvedapparatus (devices) for generating electrical energy based on thePeltier/Seebeck effect and methodologies for constructing such devices.

Selected combinations of aspects of the disclosed technology correspondto a plurality of different embodiments of the presently disclosedsubject matter. It should be noted that each of the exemplaryembodiments presented and discussed herein should not insinuatelimitations of the presently disclosed subject matter. Features or stepsillustrated or described as part of one embodiment may be used incombination with aspects of another embodiment to yield yet furtherembodiments. Additionally, certain features may be interchanged withsimilar devices or features not expressly mentioned which perform thesame or similar function or functions.

Reference is made in detail herein to presently preferred exemplaryembodiments of the subject thermoelectric generators and methodologiesfor constructing such generators. With initial reference to FIG. 1,there is illustrated an exemplary assembly process generally 100 forconstructing exemplary thermoelectric generators (TEGs) in accordancewith the presently disclosed subject matter. Assembly process 100 beginswith the formation of blanks 102 of both p-type and n-type materialsthat are then formed into individual oxide thermoelectric elements asdescribed herein. As will be understood by those of ordinary skill inthe art from the complete disclosure herein, process 100, for simplicityof illustration, illustrates only a single block 102 representative ofboth p-type and n-type material blocks.

To construct a thermoelectric module such as exemplary module generally150, elements of p-type and n-type semiconducting materials arepreferably used. Such materials may be prepared from common ceramic rawmaterials, using standard ceramic engineering processing, with thefollowing general procedure.

An n-type semiconducting oxide ceramic composition in accordance withthe presently disclosed subject matter may be constructed primarily ofstrontium titanate (SrTiO3) with from 0 to 5 weight percent of addedsuch as strontium oxide, niobium oxide, lanthanum oxide, bismuth oxide,silicon dioxide, aluminum oxide, sodium oxide, tantalum oxide, neodymiumoxide, cerium oxide, molybdenum oxide, tungsten oxide and/or titaniumdioxide to create a strongly semiconducting composition. Thesecomponents may be added in the form of oxides, carbonates, nitrates,acetates or any other reagents bearing the correct cation.

Similarly, a p-type semiconducting oxide ceramic composition inaccordance with the presently disclosed subject matter may beconstructed primarily of nickel oxide with from 0 to 8 weight percent ofadded lithium oxide, sodium oxide, potassium oxide and/or bismuth oxide.Such components may be added in the form of oxides, carbonates,nitrates, acetates or any other reagents bearing the correct cation.

The n-type and p-type compositions may be separately blended andcalcined to form one or more solid solution ceramic materials which arethen milled to approximately 1 um average particle size, prior to binderaddition and green body forming operations. Alternatively, suchmaterials may be cake batched and milled in an appropriate solvent(aqueous or non-aqueous) for green formation. Following this, anappropriate binder is added and green forming is performed. In suchcase, the calcination would occur during the firing operation, formingone or more solid solution ceramic materials at that time.

A green body formation technique is then preferably utilized which willallow the formation of ceramic blanks 102 from which individual elements106 will be cut. The green body formation technique used can be selectedfrom several different choices, depending on the degree of complexityand desired properties of the final ceramic n-type or p-type element.Non-limiting examples of exemplary techniques for forming ceramic blanks102 include die-pressing, extrusion, tape casting, and wet laydown.

In an exemplary die-pressing process, the milled ceramic powder orslurry formulation may be mixed with a solution of polymers includingbinders and plasticizers, then dried and granulated to produce a drypressing feedstock. The feedstock may then be dry-pressed to form disksor plates.

In an exemplary extrusion process, the ceramic powders are combined withorganic binder system (in either an aqueous or organic solvent carrier)to form a doughlike feedstock, which may then be extruded to form rods,bars or plates of any advantageous cross-section. Such rods, bars, orplates may then be diced across their cross-section to form the ceramicblanks.

In an exemplary tape casting process, the milled ceramic slurry may becombined with a binder solution system to form a slip. The ceramic slipsare tape cast into layers ranging from 0.5 micron up to 100 microns ormore. Such layers may be stacked to the desired thickness and thenlaminated, forming green ceramic pads, which may be saw-diced orblade-diced to form the ceramic blanks.

In an exemplary wet laydown process, the milled ceramic slurry iscombined with a binder solution system to form a somewhat differentslip, which may be successively applied to a carrier plate and dried.Representative non-limiting examples of application methods of the slipto the carrier include, for example, doctor blading, screen printing,spraying, or waterfall casting. In such manner, a pad of the correctthickness is built up on the carrier plate. The final pad is dried andmay be diced to form ceramic blanks 102 either before or after releasefrom the carrier plate.

Because each of such exemplary alternative methods can allow formultiple layers to be combined into the green body, a highly engineeredceramic body with controlled composition and microstructure may beformed. A benefit of such green-body fabrication techniques is that avariety of features may easily be incorporated into the thermoelectricelements, i.e. the elements may be “engineered”. These features include,without limitation, dispersion of fine porosity to reduce thermalconductivity while largely maintaining low electrical conductivity;dispersion of discrete metal particles, especially at the “ends” of theelement to facilitate joining of elements to metallized substrates;incorporation of floating tab electrodes, similar to so-called dummyelectrodes (anchor tabs) used in Fine Copper Termination (FCT) to helpanchor external metallization to the “ends” of the elements; and gradedand/or lamellar structures that may be employed to create non-uniformconcentrations of porosity, metallization and/or chemical compositiontypically, but not exclusively, along the axis perpendicular to theend-caps of the device. It should be appreciated by those of ordinaryskill in the art that combinations of these features can be used tomanipulate thermal expansion properties to reduce stress gradientsbetween dissimilar materials. Attributes obtained from such engineeredelements include achievement of low thermal conductivity, highelectrical conductivity, and durable high-temperature bonds betweenelement and substrate.

It should also be appreciated by those skilled in the art that thesetechniques might be applied to any other material or combination ofmaterials which may be prepared in a powder form and when thermallytreated, will form a material with thermoelectric properties. Forexample, barium strontium niobate has been prepared in a ceramic formand has been shown to exhibit interesting thermoelectriccharacteristics. The powder forms of barium strontium niobate precursorsand dopants (e.g. niobium or lanthanum oxides) may be combined andformed using the above processes, producing similar microstructuralfeatures.

Metal particles such as nickel, copper, silver, palladium, etc., may beadded to the slip or feedstock to create a ceramic/metal composite ingiven layers, particularly outer contact surfaces. Such metal particleaddition is advantageous for creating improved electrical contact withexternal metallization and/or for matching thermal expansion of elementsand contacting substrates or headers.

A slip or feedstock with an excess of donor ions for n-type materialsand acceptor ions for p-type materials may be used to heavily dope theouter layers of the blanks, where external metallization may be broughtin contact with the materials. Heavy doping may be used to achievestrongly ohmic contacts in semiconductors.

Small electrode tabs may be incorporated into the surface of theelement, which, when exposed by dicing or polishing, will improve theintimacy of contact between the external metallization and the ceramic,and provide anchoring points for applied external metallization layers.In accordance with the presently disclosed subject matter, suchmetallization layers may be applied using plating, sputtering,evaporation, screen printing techniques, or other known or futuredeveloped processes.

Tape casting and wet buildup are presently generally preferred methodsfor some embodiments as such methods generally provide greater thicknesscontrol and finer resolution than can be achieved using other methods.Other methods may, however, be employed depending on the precisionrequired for construction of particular embodiments of the presentlydisclosed subject matter.

It should be noted that at this point, like many conventional ceramicelectronic components, elements near their final size could be directlydiced from the pads or blanks, rather dicing as blanks, firing theblanks and dicing the fired blanks into elements. The eventual inclusionof blank lapping is advantageous to providing the dimensional controlfor later alignment of the elements between headers.

Following green forming the organic binders may be removed from theblanks using standard burnout techniques. Blanks containing only ceramicpowder or ceramic powder and polymer microspheres may be burned out inair at temperatures of up to 750° C. using slow ramp rates, for example,on the order of 2° C. per minute. Blanks containing metal powders may beburned out in air or in reducing atmosphere depending on therequirements of the metal to avoid deleterious oxidation or reductionreactions. Removal of nearly all of the organic material is generallydesirable as remaining carbon may influence the furnace atmosphereduring firing, or cause delamination or other green defects duringfiring. A single layer of parts on each setter is generally recommended.

The blanks 102 may then be fired to densify the body, create the desiredmicrostructure, and distribute the dopants to yield a stronglysemiconducting body. Each ceramic composition generally has its ownpreferred firing profile. For example, the strontium titanate-basedn-type material typically would be fired at temperatures ranging from1275 to 1400° C. for 2 to 16 hours in a reducing atmosphere with oxygenpartial pressures ranging from 10-6 to 10-18 atm. The nickel oxidep-type ceramic typically would be fired at temperatures ranging from1225 to 1400° C. for 1 to 4 hours in an air or otherwise oxidizingenvironment.

During firing, minimization of the amount of camber in the fired blanksis important. For example, following burnout, the blanks may bepositioned on the firing setters and covered with weighted plates toencourage flatness. Alternatively, blanks may be fired in stacks as atechnique for generally maintaining flatness during firing. Maintainingflatness allows the ceramic to be more easily polished to a consistentthickness. Also, firing in stacks or surrounding the material with asimilar composition of ceramic assists in controlling the loss of anyvolatile components from the blanks (e.g. lithium from NiO) to thesetters or furnace environment.

Individual elements 106 may be cut from the fired blanks 102 or fromplated blanks 104. During module construction, elements 106 may besandwiched between two metallized insulators or “headers.” Becauseelements 106 generally are to be aligned with contacts in the sameplane, it is preferable to maintain dimensional control over them insuch direction. As noted, individual elements can also be cut fromgreenware, prior to firing. This substantially avoids issues related tocamber, but requires appropriate fired dimensional control and suitabletermination procedures.

Maintenance of dimensional control may be achieved in several ways. Inaccordance with exemplary such ways, the fired blanks may be lapped, forexample using double-sided grinding, to a consistent thickness. Suchprocess may be advantageous when metal or additional doping is used inthe outer layers for electrical contact or bonding purposes. In suchcase, the substrates will be metallized as represented by structure 104after the lapping procedure but before the element dicing procedure.

Alternatively, the blanks may be diced such that the thickness of theelement is dictated by the lateral dimension during dicing. Suchtechnique is advantageous when tab electrodes are created in the blankand are exposed by dicing, again to enhance bonding and contact. In suchcase, the parts will be diced into strips to expose the tabs and the tabsurfaces would then be metallized. After surface metallization, anadditional dicing to singulate the elements 106 from the strips wouldpreferably be performed.

The desired metallization may then be applied to the correct surfaces.It is preferable per the presently disclosed subject matter to selectmetallization which yields a strong ohmic contact, with good mechanicaladhesion. The desired procedure typically starts with a rigorouscleaning procedure using solvents such as alcohols and acetone, andceramic etchants such as fluoboric acid and hydrogen peroxide, followedby thorough drying.

Metallization preferably may then proceed as follows. For the n-typestrontium titanate elements, a sputter etch may be performed, followedby a sputtered layer of, for example, 1000 angstroms oftitanium-tungsten. Such step is followed by a layering of, for example,1000 angstroms of nickel which may contain some vanadium. Finally, thenickel layer may be capped by approximately 100 angstroms of sputteredgold. Such layers serve as an adhesion layer on which other surfacemetallization may be deposited, for example by electroplating. In anexemplary construction, an electroplated layer may be approximately10-25 microns thick and may correspond to copper, silver, gold, nickel,nickel-phosphorus or any metal producing a relatively low resistancecontact and favorable bonding with the header metallization.

For the p-type nickel oxide elements, various methods may be used tocreate an adhesion layer. In a first exemplary method, cleaned surfacesmay be activated with palladium and then coated with copper viaelectroless plating. In an exemplary configuration, the copper platingmay be 0.5 to 5 microns thick. In a second exemplary configuration, asputter etch may be performed followed by application of a sputteredlayer of nickel that optionally contains some vanadium, and a sputteredlayer of gold. In an exemplary configuration, the nickel layer may beabout 1000 angstroms thick while the gold layer may be about 100angstroms thick. Following either of such approaches, contactmetallization may again be deposited, for example by electroplating, toapproximately 10-25 microns thick, and again may consist of copper,silver, gold, nickel, or any metal producing a low resistance contactand favorable bonding with the header metallization.

The n-type or p-type elements may then be diced from such substrates todimensions giving adequate thermal insulation and low electricalresistance. In exemplary configurations, size may range from 125 micronsin length, width and height to greater than 3 millimeters in eachdimension, and may resemble such as rods, bars, or cubes. The dicingprocedure should preferably result in electroded surfaces on oppositesides of each element, for property testing and eventual moduleconstruction.

With further reference to FIG. 1, thermoelectric modules generally 150are assembled from p-type and n-type representative elements 106 wherethe elements 106 are typically of uniform size and properties. Elements106 are arranged in pairs of p-type 108 and n-type 110 elements whichare connected in series, for example, by way of representativeconductive traces 112 on substrate 114. Configurations may also be usedthat combine series/parallel electrical connection—in order tomanipulate device resistance (desirably low) while elements arethermally in parallel. In such manner, each couple contributes acharacteristic amount of voltage for a given temperature differencebetween hot and cold surfaces which add together to yield the totalvoltage produced by the module. Because the elements are connected inseries, the resistance for each couple also is additive; however, suchresistance is detrimental to the overall power output by the module. Itis, therefore, relatively important in preparing modules to preferablyavoid as possible any increase in the overall resistance during theassembly of the modules 150.

With continued reference to FIG. 1, an exemplary procedure isrepresented for preparing sandwich-type modules consisting of one ormore unicouples composed of oxide ceramic elements. In an exemplary suchmethodology in accordance with the presently disclosed subject matter,headers 114, 116, or ceramic substrates, with appropriate metallizations(representatively metallizations 112, 118), are fabricated from suitablematerials including, for example and without limitation, aluminum oxide,aluminum nitride or other relatively high thermal conductivity,electrically insulating ceramic substrates. In exemplary configurations,such substrates may be formed with thicknesses typically ranging from250 to 625 microns. Metallization can be applied by either thick film(screen printing/firing) or thin film (sputtering, evaporation, plating)techniques.

On one surface of each header 114, 116, the metallization 112, 118 maybe preferably patterned to form the series connection between elements108, 110, while generally a complete sheet of metallization will beapplied to the other. Such approach is meant to facilitate thermaltransfer between the heat source and the module on the hot side, and tofacilitate heat removal from the cold side by adjunct or associatedcooling reservoirs, coils, fins or air flow (not separately illustrated,details of which form no particular aspect of the presently disclosedsubject matter). Such metallization may facilitate the physical bondingof heating and/or cooling structures to the presently disclosedexemplary module.

In exemplary configurations of thick film metallization, copper, nickel,silver, silver, palladium, platinum, or gold pastes, or pastes composedof alloyed powders of such, may be used. The selection would generallydepend on the resistance desired and the type of bonding between elementand header, or heat exchanging structure and header, for a particularembodiment. The selection would also dictate the firing profile neededto bond the metallization to the header.

In exemplary configurations of thin film metallizations, substrates arerigorously cleaned using solvents such as alcohols and acetone, andceramic etchants such as fluoboric acid and hydrogen peroxide, followedby thorough drying. Following such step, a sputter etch may beperformed, followed by applying a sputtered layer, such as of 1000angstroms of titanium-tungsten. Such step is followed by 1000 angstromsof nickel (containing some vanadium), which is capped by approximately100 angstroms of sputtered gold. Such layers serve to act as an adhesionlayer, on which other surface metallization may be electroplated.Electroplating is approximately 5-25 microns thick, and may consist ofcopper, silver, gold, nickel, or any metal producing a relatively lowerresistance contact and favorable bonding with the element metallization.

While the above-described thin film method is one presently favored,other adhesion layer materials may also be used. For example,copper-chromium-gold layers of metallization are known to provide goodadhesion to ceramic substrates and devices. Also, a fired thick filmlayer may provide a well-adhered base for a plated layer of the variousmetals mentioned above.

Whereas screen printing thick film materials will provide the correctpattern to create the series connection for the ceramic elements, thethin film materials likely are patterned either by masked deposition orby conventional photolithographic techniques.

To begin module assembly, a method of alignment is selected to place then-type and p-type parts in alternating positions directly over theirmetallized locations on the headers. Alignment may be accomplished in anumber of ways including, without limitation, using alumina or graphitespacer bars or alignment forms with holes drilled at the appropriatelocations. An appropriate bonding material (preform or paste) shouldalso be placed on, or applied to, the metallization prior to elementplacement.

Because the modules will likely be better used with at least thehot-side header at temperatures exceeding 500° C., high temperatureappropriate bonding techniques are preferably used for assembly. Also,effective use of the ceramic elements may, in some instances, requirethat the cold side exceed 150° C., which would prohibit use of a varietyof low temperature brazes or solders. In accordance with the presentlydisclosed subject matter, several techniques may be used, including,without limitation: brazing both hot and cold sides simultaneously,using braze filler materials such as alloys of primarily copper andsilver; and brazing hot and cold sides separately, allowing a hightemperature bonding material such as a copper-silver alloy to be used onthe hot side and a lower temperature alloy (such as high lead solder) tobe used on the cold side. Additionally, copper-copper thermocompressionbonding may be employed on at least the hot side of the module. Suchprocess requires that copper surface layers be present during bondingand that the elements be uniform in size so that the pressure is uniformthroughout each bonded surface.

Termination paste bonding involves use of a copper, nickel, silver, oralloy termination paste as the bonding medium between the element andthe header. Such procedure offers several advantages including creatinga bond that is stable at higher temperatures than available from brazingpastes, and the possibility of engineering the composition to minimizethermal stresses between the element and the header. However, it ispreferable that excellent density is achieved in the contact region toachieve good electrical and thermal transport.

With continued reference to FIG. 1, bonding pads 120, 122 are providedon the cold side header 116 where wires, pins, or other devices (notseparately illustrated, and details of which form no particular aspectsof the present subject matter) may be soldered or brazed to allowconnection of the module to either an electrical load which will use thethermoelectric power generated or to other thermoelectric generators inseries to increase the voltage or current and therefore the overallpower generated by the assembly.

It should be appreciated from the above that the construction sequenceillustrated in FIG. 1 provides for separately forming n-type and p-typeelements generally illustrated as element 106 by first forming separateblanks 102 from appropriate materials as previously described and then,optionally, metalizing blank 102 to produce a plated blank 104 which maythen be singulated into individual elements 106. Pairs 108, 110 of thesingulated elements are then arranged over and secured to metallizations112 on header 114. Header 114 is then “flipped over” as indicated byarrow 130 and aligned over header 116 which has applied theretometallizations 118 including terminal connections 120, 122. When theindividual elements 106 are electrically connected to metallizations118, the result is a series connection of a plurality of element pairs.In such configuration, each element pair provides a characteristicvoltage output dependent on, among other things, the composition of theelements and the temperature difference between the hot side header 114and the cold side header 116.

To improve the power output of the device in operation, the highestlevel of thermal contact between the exterior surfaces of the headersand the heat exchanging surfaces on the hot and cold side shouldpreferably be maintained. Thermal interface materials such as metalsheets, thermal greases, graphite papers, and similar products may beused to improve the thermal contact, allowing more thermal energy to betransmitted to and taken away from the ends of the elements.

With reference now to FIGS. 2A-2C (generally FIG. 2), there isillustrated an alternative embodiment generally 200 of the presentlydisclosed subject matter employing screen-printed substrates. Asillustrated, screen-printed copper paste 202 is applied to the top andbottom surfaces of substrate 204. The bottom (unseen) surface may haveapplied thereto copper paste in a configuration that, in conjunctionwith the illustrated top surface copper paste configuration, will resultin an electrical connection of elements 208, 210 into serial connectedpairs. An exemplary configuration of the unseen configuration on thebottom surface of substrate 204 may be similar to the metallizations 112illustrated in FIG. 1 as applied to substrate 114. In accordance withthe exemplary embodiment of FIG. 2, substrate 204 may be an Al2O3substrate.

During construction of the exemplary embodiment of FIG. 2, the variouselements 208, 210 are put in place preferably while the copper paste isstill wet, and a top and bottom sandwich 250 is assembled. The sandwichis dried in an alignment fixture (not separately illustrated) and, afterdrying is removed from the alignment fixture and fired to form copper tocopper bonds. Leads may then be attached to connection terminals(representatively illustrated in FIG. 1 as terminals 120, 122).

With reference now to FIGS. 3A-3D, there are illustrated respectiveadditional alternative configurations that may be produced using thesame p-type and n-type materials previously described. FIG. 3Aillustrates an exemplary radial configuration wherein the “hot side” iscentrally located and the “cold side” is on the perimeter of the device.Such an embodiment may be used advantageously for example with heatsources such as a fire or heat from a vehicle exhaust system. FIG. 3Billustrates another exemplary radial structure employing p-type andn-type tubing separated by ceramic rings. FIG. 3C illustrates anexemplary embodiment wherein the hot side of the elements 308, 310 aredirectly brazed together while the cold side of the elements 308, 310are soldered to substrate 314. The FIG. 3D exemplary embodiment of thepresently disclosed subject matter incorporates a mechanical retentionmechanism (nuts and bolts 320) to produce a device that requires neitherbrazing nor soldering to retain the p-type and n-type elements in solidcontact with each other.

As will be understood by those of ordinary skill in the art from thecomplete disclosure herewith, the presently disclosed subject matter maybe particularly useful for adaptation for use in a variety ofconfigurations where temperature differentials may be leveraged. Suchmay include, for example, pipe-mounted configurations such as for remotesensing, integrated into a wood fuel stove (either involving naturalwood or pelletized wood), integrated into a gas stove for either such ascommercial or military use, associated with an industrial furnace flue,associated with an automobile or other internal combustion engineexhaust system, or associated with a municipal or commercial solid wastedisposal/generator. Also, while various applications may be practiced,variations of modules resulting from different configurations may bepracticed, for creation of modules such as adapted for generatingseveral Watts or more of power, and for operating with hot sidetemperatures on the order of 300 to 800 degrees C., with temperaturedifferentials (ΔT) of 100 degrees C. or higher.

While the presently disclosed subject matter has been described indetail with respect to specific embodiments thereof, it will beappreciated that those skilled in the art, upon attaining anunderstanding of the foregoing may readily produce alterations to,variations of, and equivalents to such embodiments. Accordingly, thescope of the present disclosure is by way of example rather than by wayof limitation, and the subject disclosure does not preclude inclusion ofsuch modifications, variations and/or additions to the presentlydisclosed subject matter as would be readily apparent to one of ordinaryskill in the art.

What is claimed is:
 1. A thermoelectric device for converting thermalenergy to electrical energy based on temperature differences betweenportions of the device, comprising: a plurality of N-type oxide ceramicelements; a plurality of P-type oxide ceramic elements, respectivelypaired with said plurality of N-type elements; a pair of supportingceramic substrates, supporting a plurality of conductive traces thereon,and with said paired N-type and P-type elements received on selected ofsaid conductive traces so as to form an array of such pairs between saidsubstrates; and at least one pair of connection terminals provided on atleast one of said substrates, for the connection of leads thereto;wherein said paired elements are electrically connected in series bysaid conductive traces and thermally connected in parallel relative tosaid substrates, so that generated electricity may be conducted fromsuch array based on temperature differences between portions of saidpaired elements based on the Peltier/Seebeck effect.
 2. A thermoelectricdevice as in claim 1, wherein said substrates comprise planarconstructions forming a sandwich of said array of paired elementsbetween said substrates.
 3. A thermoelectric device as in claim 2,wherein said conductive traces comprise screen-printed, fired thickpaste materials on at least one of said substrates.
 4. A thermoelectricdevice as in claim 2, wherein said conductive traces comprisecomplementary patterns of screen-printed, fired metallizations formed onsaid substrates.
 5. A thermoelectric device as in claim 2, wherein: saidN-type elements comprise SrTiO3 material incorporating doping material;and said P-type elements comprise NiO material incorporating dopingmaterial.
 6. A thermoelectric device as in claim 5, wherein: said dopingmaterial for said N-type elements comprises at least one of Nb and La;and said doping material for said P-type elements comprises at least Limaterial.
 7. A thermoelectric device as in claim 1, wherein saidplurality of N-type and P-type elements comprise at least one of gradedand lamellar structures which create non-uniform concentrations of atleast one of porosity, metallization, and chemical composition of saidelements, to provide selected thermal expansion and bonding propertiesof said elements.
 8. A thermoelectric device as in claim 1, wherein saidplurality of N-type and P-type elements each respectively havedimensions in length, width, and height ranging from about 125 micronsto at least 3 millimeters.
 9. A thermoelectric device as in claim 1,further including bonding material between said elements and saidconductive traces, respectively.
 10. A thermoelectric device as in claim1, wherein said substrates comprise ceramic rings forming concentricradial configurations having a generally open central portion adaptedfor exposure to a heat source with the exterior portion of thethermoelectric device adapted for exposure to an environment cooler thansaid heat source.
 11. A thermoelectric device as in claim 10, whereinsaid conductive traces include brazing for one of the ends of saidpaired elements.
 12. A thermoelectric device for converting thermalenergy to electrical energy using electrically coupled dopedsemiconductive ceramic elements to generate electricity based ontemperature differences between portions of the device, comprising: aplurality of N-type elements, each comprising a doped semiconductiveoxide ceramic element; a plurality of P-type elements, each comprising adoped semiconductive oxide ceramic element, respectively paired withsaid plurality of N-type elements; a pair of supporting ceramic ringsforming concentric radial configurations having a generally open centralportion adapted for exposure to a heat source with the exterior portionof the thermoelectric device adapted for exposure to an environmentcooler than said heat source, and with said paired N-type and P-typeelements received on selected portions of said ceramic rings so as toform a radial array of such pairs; and electrical connections forelectrically connecting said paired elements in series while said pairedelements are thermally connected in parallel relative to said ceramicrings, so that generated electricity may be conducted from such arraybased on temperature differences between portions of said pairedelements based on the Peltier/Seebeck effect.
 13. A thermoelectricdevice as in claim 12, further including mechanical retention mechanismfor holding said paired elements in mutual contact.
 14. A thermoelectricdevice as in claim 13, wherein said mechanical retention mechanismincludes at least one matching bolt and nut.
 15. A thermoelectric deviceas in claim 12, wherein said electrical connections further includebrazing for one of the ends of said paired elements and soldering forthe other of the ends of said paired elements.
 16. Thermoelectricgenerator module for converting thermal energy to electrical energyusing electrically coupled doped semiconductive ceramic elements togenerate electricity based on temperature differences between portionsof the module based on the Peltier/Seebeck effect, comprising: aplurality of N-type elements, each comprising a doped semiconductiveoxide ceramic element; a plurality of P-type elements, each comprising adoped semiconductive oxide ceramic element, respectively paired withsaid plurality of N-type elements; an opposing pair of generally planarsupporting ceramic substrates, supporting a plurality of complementaryconductive traces thereon, and with said paired N-type and P-typeelements received on selected of said conductive traces so as to form anarray of such pairs sandwiched between said substrates; and at least onepair of connection terminals provided on at least one of saidsubstrates, for the connection of leads thereto; wherein said pairedelements are electrically connected in series by said conductive tracesand thermally connected in parallel relative to said substrates, so thatgenerated electricity may be conducted from such array via saidconnection terminals based on temperature differences between portionsof said paired elements.
 17. A thermoelectric generator module as inclaim 16, wherein said conductive traces comprise complementary patternsof screen-printed, fired metallizations formed on said substrates.
 18. Athermoelectric generator module as in claim 16, wherein: said N-typeelements comprise SrTiO3 material incorporating doping materialcomprising at least one of Nb and La; and said P-type elements compriseNiO material incorporating doping material comprising at least Limaterial.
 19. A thermoelectric generator module as in claim 16, whereinsaid plurality of N-type and P-type elements comprise at least one ofgraded and lamellar structures which create non-uniform concentrationsof at least one of porosity, metallization, and chemical composition ofsaid elements, to provide selected thermal expansion and bondingproperties of said elements.
 20. A thermoelectric generator module as inclaim 16, wherein said plurality of N-type and P-type elements eachrespectively have dimensions in length, width, and height ranging fromabout 125 microns to at least 3 millimeters.
 21. A thermoelectricgenerator module as in claim 16, further including bonding materialbetween said elements and said conductive traces, respectively. 22.Methodology for generating electrical energy based on thePeltier/Seebeck effect using oxide ceramic elements by providing athermoelectric module constructed by coupling N-type and P-typematerials as individual elements to form pairs electrically connected inseries and thermally in parallel between opposing supporting substrates.23. Methodology as in claim 22, further including using one of thick andthin film manufacturing techniques to selectively produce metallizationsserving as electrical interconnections for said individual elementscapable of performing with relatively higher temperatures. 24.Methodology as in claim 22, wherein said supporting substrates havescreen-printed metallizations for electrically coupling said individualelements.
 25. Methodology as in claim 22, wherein said individualelements comprise p-type and n-type semiconducting materials preparedusing standard ceramic engineering processing.
 26. Methodology as inclaim 25, wherein: said n-type semiconducting material comprises ann-type semiconducting oxide ceramic composition constructed primarily ofstrontium titanate (SrTi03) with from 0 to 5 weight percent of addedstrontium oxide, niobium oxide, lanthanum oxide, bismuth oxide, silicondioxide, aluminum oxide, sodium oxide, tantalum oxide, neodymium oxide,cerium oxide, molybdenum oxide, tungsten oxide and/or titanium dioxide;and said p-type semiconducting material comprises a p-typesemiconducting oxide ceramic composition constructed primarily of nickeloxide with from 0 to 8 weight percent of added lithium oxide, sodiumoxide, potassium oxide and/or bismuth oxide.
 27. Methodology as in claim22, wherein said individual elements comprise p-type and n-typesemiconducting materials prepared using ceramic blanks from which saidindividual elements are cut, with said ceramic blank formed from greenbody formation techniques.
 28. Methodology as in claim 27, wherein saidgreen body formation techniques comprise at least one of die-pressing,extrusion, tape casting, and wet laydown.
 29. Methodology as in claim27, wherein said green body formation techniques include the use of atleast one of graded and lamellar microstructures within said pluralityof N-type and P-type individual elements so as to selectively createnon-uniform concentrations of at least one of porosity, metallization,and chemical composition of said elements, to provide selected thermalexpansion and bonding properties of said elements, to facilitatecreation of modules adapted for operating with high temperatures in arange of from about 300 to 800 degrees C., and with temperaturedifferentials (ΔT) of at least 100 degrees C.
 30. Methodology as inclaim 22, further including providing an adhesion layer respectivelybetween said individual elements and electrical connections thereof. 31.Methodology as in claim 22, wherein said individual N-type and P-typeelements each respectively have dimensions in length, width, and heightranging from about 125 microns to at least 3 millimeters. 32.Methodology as in claim 22, wherein said supporting substrates compriseplanar headers supporting selected arrangements of metallized portionsthereon, and said methodology further includes aligning and placing saidindividual N-type and P-type elements in respective alternatingpositions directly inline with their metallized portions on saidheaders.
 33. Methodology as in claim 32, further including one ofsimultaneously and separately brazing both headers to said individualelements, with selected materials for specific temperature responsiveperformance.
 34. Methodology as in claim 22, further including providingbonding pads on at least one of said supporting substrates, electricallyconnected so to allow connection of the module to either an electricalload which will use the thermoelectric power generated or to otherthermoelectric modules in series to increase the voltage or current andtherefore the overall power generated.
 35. Methodology as in claim 22,wherein said supporting substrates form a concentric radialconfiguration wherein a central location of said radial configuration isintended for exposure to a heat source while radially outward portionsof said configuration are intended for relatively lower temperaturesources.
 36. Methodology as in claim 35, wherein one end of the pairs ofN-type and P-type materials individual elements are directly brazedtogether while the other end of the pairs of said elements are solderedto a radially outward one of said substrates.
 37. Methodology formanufacturing a thermoelectric generator module for converting thermalenergy to electrical energy using electrically coupled dopedsemiconductive oxide ceramic elements to generate electricity based ontemperature differences between portions of the module based on thePeltier/Seebeck effect, comprising: providing an opposing pair ofgenerally planar supporting ceramic substrates, supporting a pluralityof complementary conductive traces thereon; placing an array of pluralpaired N-type elements and P-type elements in electrical communicationwith said conductive traces so that the paired elements are electricallyconnected in series by said conductive traces, said elements eachcomprising a doped semiconductive oxide ceramic element, and such thatsaid elements are thermally connected in parallel relative to saidsubstrates; and attaching at least one pair of connection terminals onat least one of said substrates, for the connection of leads thereto, sothat generated electricity may be conducted from such array via saidconnection terminals based on temperature differences between portionsof said paired elements.
 38. Methodology as in claim 37, said conductivetraces are formed by patterns of screen-printed, fired metallizationsformed on said substrates.
 39. Methodology as in claim 37, wherein: saidN-type elements comprise SrTiO3 material incorporating doping materialcomprising at least one of Nb and La; and said P-type elements compriseNiO material incorporating doping material comprising at least Limaterial.
 40. Methodology as in claim 37, further including selectivelyproviding at least one of graded and lamellar structures within saidplurality of N-type and P-type elements so as to selectively createnon-uniform concentrations of at least one of porosity, metallization,and chemical composition of said elements, to provide selected thermalexpansion and bonding properties of said elements.
 41. Methodology as inclaim 37, wherein said plurality of N-type and P-type elements eachrespectively have dimensions in length, width, and height ranging fromabout 125 microns to at least 3 millimeters.
 42. Methodology as in claim37, further including providing bonding material between said elementsand said conductive traces, respectively.
 43. A method of providing athermoelectric device for converting thermal energy to electrical energybased on temperature differences between portions of the device,comprising: forming respective pluralities of N-type and P-type oxideceramic elements; providing a pair of ceramic substrates with aplurality of predetermined conductive traces thereon; respectivelypairing and aligning said N-type and P-type elements on selected of saidconductive traces so as to form an array of such pairs electricallyconnected in series and captured between said substrates and thermallyconnected in parallel between opposing determined hot and cold sidesthereof; and forming at least one pair of connection terminals on atleast one of said substrates, for the connection of leads thereto, sothat generated electricity may be conducted from such array based ontemperature differences between such hot and cold sides based on thePeltier/Seebeck effect.
 44. A method as in claim 43, wherein saidsubstrates comprise one of planar constructions forming a sandwich ofsaid array of paired elements between said substrates, and ceramic ringsforming concentric radial configurations having a generally open centralportion adapted for exposure to a heat source with the exterior portionof the thermoelectric device adapted for exposure to an environmentcooler than said heat source.
 45. A method as in claim 43, wherein saidconductive traces are formed by screen-printed, fired metallizations onsaid substrates.
 46. A method as in claim 43, wherein: said N-typeelements comprise SrTiO3 material incorporating doping materialcomprising at least one of Nb and La; and said P-type elements compriseNiO material incorporating doping material comprising at least Li.
 47. Amethod as in claim 43, wherein said plurality of N-type and P-typeelements are formed of at least one of graded and lamellar structureswhich create non-uniform concentrations of at least one of porosity,metallization, and chemical composition of said elements, to provideselected thermal expansion and bonding properties of said elements. 48.A method as in claim 43, further including: bonding material betweensaid elements and said conductive traces, respectively; and wherein saidplurality of N-type and P-type elements each respectively havedimensions in length, width, and height ranging from about 125 micronsto at least 3 millimeters.
 49. A method of making a thermoelectricdevice for converting thermal energy to electrical energy usingelectrically coupled doped semiconductive oxide ceramic elements togenerate electricity based on temperature differences between portionsof the device, comprising: forming a plurality of N-type elements, eachcomprising a doped semiconductive oxide ceramic element; forming aplurality of P-type elements, each comprising a doped semiconductiveoxide ceramic element, respectively paired with said plurality of N-typeelements; providing a pair of supporting ceramic rings formingconcentric radial configurations having a generally open radiallycentral portion adapted for exposure to a heat source with the radiallyexterior portion of the thermoelectric device adapted for exposure to anenvironment cooler than said heat source; placing said paired N-type andP-type elements on selected portions of said ceramic rings so as to forma radial array of such pairs; and electrically connecting said pairedelements in series while said paired elements are thermally connected inparallel relative to said ceramic rings, so that generated electricitymay be conducted from such array based on temperature differencesbetween portions of said paired elements based on the Peltier/Seebeckeffect.
 50. A method as in claim 49, wherein said electricallyconnecting includes directly brazing together the paired ends of saidpaired elements closer towards the radially central portion of saiddevice, and soldering the other of the ends of said paired elements toone of said ceramic rings.